The toxicokinetics of oxazepam were studies in F344 rats, B6C3F1 mice and Swiss mice. Elimination of oxazepam appears to be a first order process in all species. A sex difference in distribution and elimination was observed in F344 rats. At the same dosage (oral or iv), oxazepam plasma concentrations in male rats are significantly lower than in female rats. In rats, oxazepam plasma concentrations tend to increase when the oral gavage dose is increased from 50 to 200 mg/Kg. However, there was no further significant increase of plasma concentrations at 400 mg/Kg dosage, which is believed to be caused by incomplete absorption. Bioavailability of oxazepam from the gavage route is poor. The calculated bioavailability based on dose normalized are under concentration versus time curves ((AUC) values ranged from 26 to 43%. There was no obvious sex differences in bioavailability.